1. Field of the Invention
The present invention relates to a semiconductor device. More particularly, the present invention relates to a laser link structure used in semiconductor devices and a fuse box using the laser link structure.
2. Description of the Related Art
In general, in order to increase yield, a semiconductor device includes normal memory cell arrays and redundancy memory cell arrays, in which a normal memory cell having defects (hereinafter, ‘defective cell’) is replaced with a redundancy memory cell (hereinafter, ‘redundant cell’).
As is well known in the art, a semiconductor memory device includes a redundancy circuit for replacing a defective cell with a redundant cell. The redundancy circuit includes program means for programming the address of a defective cell and a predetermined control circuit for controlling the redundancy circuit. The program means includes a plurality of fuses that decode the address of a defective cell using laser or an electric current so as to replace the defective cell with a redundant cell. The program means is generally called a ‘fuse box.’
In general, fuses are formed of polysilicon fuses or make-links. Make-links are also called ‘laser links.’ However, in the event that fuses are formed of polysilicon, the layout area of a fuse box is increased. For this reason, recently, fuses formed of make-links are preferred.
FIG. 1 illustrates a view of a layout of a conventional laser link structure. FIG. 2 illustrates a cross-sectional view of the conventional laser link structure of FIG. 1, taken along section line X-X′.
Referring to FIGS. 1 and 2, a first plasma-enhanced TEOS (PTEOS) layer 23, a first nitride layer (SiN) 25, a first conductive line pattern 11, a second PTEOS layer 27, and a second nitride layer (SiN) 29 are sequentially formed on a silicon wafer 21. Second conductive line patterns 13 are formed on the first conductive line pattern 11. A laser beam is scanned over a hole region 15 so as to link the first conductive line pattern 11 with the second conductive line patterns 13.
More specifically, if a laser beam is scanned over the hole region 15 for a predetermined time, the laser beam is focused on the first conductive line pattern 11, causing thermal energy to penetrate the first conductive line pattern 11. As a result, the first conductive line pattern 11 expands, and lower cracks form therein, thus resulting in the first conductive line pattern 11 being linked with the second conductive line patterns 13.
Disadvantageously, upon application of a laser beam of a relatively high energy to hole region 15, either the sides of the second conductive line pattern 13 may break or cracks may form in the second conductive line pattern 13. In this case, the first conductive line pattern 11 would not be properly linked with the second conductive line pattern 13.
Additionally, there is a limit in reducing the area of the fuse box since the energy window of a laser beam is narrow. In other words, if a distance between a first conductive line pattern 11 and another first conductive line pattern 11, i.e., a fuse pitch, is reduced, the size of the hole region 15 is also reduced. This leads to a reduction in the energy window of the laser beam when the high-energy laser beam is scanned over the hole region 15.